1. Field of the Invention
The invention generally relates to a backlight module and a light guide plate thereof. Particularly, the invention relates to a backlight module and a light guide plate suitable for keyboard of laptop computer to reduce light leakage.
2. Description of the Prior Art
As the technology advances and the specifications of the laptop computer become more critical, backlit keyboards have gradually become the major input device of the laptop computer. The backlit keyboard generally includes a keyswitch module on top and a backlight module on the bottom. The size of the backlight module is very close to that of the keyswitch module, so that the backlight module can be distributed under the keyswitch module to provide uniform brightness for different areas of the entire keyboard.
However, (1) in order to allow air to more smoothly flow from below the backlight module to above the backlight module so as to prevent the backlight module from obstructing the heat dissipation of the heat sources of the laptop computer (e.g. microprocessor, north/south bridge chip set, video chipset), (2) in order to mount the entire backlit keyboard on the laptop computer by screws that penetrate the backlight module, or (3) in order to form a plurality of recesses or openings on the backlight module to fulfill the mechanical design, the backlight module generally has a plurality of heat dissipation holes, screw holes, or openings. However, as shown in FIGS. 1A and 1B, the heat dissipation hole or screw hole 1010 of the conventional backlight module 1000 is a perfectly aligned and integrated through hole constituted by circular holes 1001˜1003 of different layers, resulting in large amount of light entering the circular through hole 1010 and leaking from the circular through hole 1010. Consequently, the light leaking from the circular through hole 1010 will cause non-uniform brightness distribution across the entire keyboard. For example, the character shown on the keycap near the through hole 1010 is brighter than the characters on keycaps at other locations.
Therefore, how to effectively improve the light leakage from the through hole or the recessed opening is an important issue.